1. Field of the Invention
The present invention relates to an objective lens driving apparatus used with an optical pickup, and according to one aspect of the invention, to an objective lens driving apparatus used with an optical pickup having an improved arrangement structure including an elastic support member supporting a blade on which an objective lens is mounted to be capable of elastically moving.
2. Description of the Related Art
In general, optical pickups record or reproduce information on or from a disk, a recording medium, by emitting light thereon. The light emitted from the optical pickup must be perpendicularly incident on a recording surface of a disk to form a light spot with the most accurate focus. If a light incident direction is inclined, an accurate light spot cannot be formed on the disk so that an error may occur during recording and reproduction of data. Thus, to form a light spot accurately on a desired track, the light must be perpendicularly incident on the recording surface of the disk. The adjustment of the light to be perpendicularly incident on the recording surface of the disk is referred to as tilt adjustment or skew adjustment. Typically, an optical pickup apparatus includes a servo-mechanism controlling the position of the objective lens in a focusing direction and a tracking direction so that the focus of light can be accurately formed on a desired track of a recording surface of a disk. However, while the servo-mechanism controls the focus of a light spot by maintaining a predetermined distance between the objective lens and the recording surface of the disk and the light spot to trace a desired track, it does not directly control the incident angle between the light and the recording surface of the disk. Thus, for more accurate recording and reproduction, a way to dynamically control the tilt is needed.
To meet the above demand, one type of objective lens driving apparatus for an optical pickup, as shown in FIG. 1, has been suggested. The optical pickup is a servo-mechanism to control the position of an objective lens 1 and includes a focus control mechanism 100 driving a blade 2. The objective lens 1 is mounted in a focus direction A, a tracking control mechanism driving the blade 2 is mounted in a tracking direction B, and a tilt control mechanism driving the blade 2 is mounted in a tilt direction C.
The focus and tracking control mechanisms are formed by a pair of focus coils 3a and 3b, a tracking coil 4, and a magnet 6. Thus, during control, an electromagnetic force driving the blade 2 in a corresponding direction is generated by applying current to the focus coils 3a and 3b and the tracking coil 4.
The tilt control mechanism can be formed separately from the focus and tracking control mechanisms. However, as shown in FIG. 1, the tilt control mechanism can be formed to be also used as the focus control mechanism. That is, during tilt control, an electromagnetic force to drive the blade 2 in the tilt direction C can be generated by applying current in a different way from the current applied during control to the focus coils 3a and 3b symmetrically arranged, for example along the tracking direction B. In other words, during focus control, currents are identically applied to the left and right focus coils 3a and 3b to drive the blade 2 in the focus direction A. During tilt control, currents are applied in different directions to the focus coils 3a and 3b to drive the blade 2 in the tilt direction C.
A plurality of wires W, elastically supporting movement of the blade 2 with respect to a holder 5 are typically arranged as shown in FIGS. 2A and 2B. FIG. 2A shows part of the structure of FIG. 1 in a simple form for the convenience of explanation. However, in this wire arrangement, a possibility exists that the position of the blade 2 becomes unstable during driving of the blade when the tilt is high. That is, as shown in FIG. 2B, three pairs of wires W1 and W6, W2 and W5, and W3 and W4 are arranged to face each other with respect to a point P which is the center of rotation when the blade 2 is being driven in a tilt direction C. Among these wire pairs, two pairs i.e. W1 and W6, and W3 and W4, have the same distance therebetween (d1=d3), while the other pair i.e. W2 and W5 has a different distance therebetween (d2≠d1=d3).
In this structure, it is assumed that the blade 2 can be moved by an angle θ by the operation of the tilt control mechanism as shown in FIG. 3A. In this case, comparing the amounts of deformation between the first and second wires W1 and W2, as shown in FIG. 3B, the amount of deformation of the first wire W1 is that r1×θ (r1=d1/2) and the amount of deformation of the second wire W2 is that r2×θ (r2=d2/2) which is less than the amount of deformation of the first wire W1. Likewise, the amounts of deformation of the third, fourth, and sixth wires W3, W4, and W6 are the same as that of the first wire W1 while the amount of deformation of the fifth wire W5 is the same as that of the second wire W2. That is, the first, third, fourth, and sixth wires W1, W3, W4, and W6 are bent to a relatively greater degree than the second and fifth wires W2 and W5 are bent.
A compression force acts on the second and fifth wires W2 and W5 so that the second and fifth wires W2 and W5 can be buckled as shown in FIGS. 4A and 4B. This is a very unstable configuration and, even if a slight vibration or impact is applied, the buckled wires can be elastically expanded so that the blade 2 may be moved in an undesired direction. Therefore, the entire system controlling the position of the objective lens 1 can become unstable. Thus, an improved structure to solve the above problem is demanded.